Antiknock compositions



United Sttes Patient Otice 2,860,958 Patented Nov. 18, 1958 ANTIKNOCK COMPOSITIONS Lewis F. Gilbert, Fraser, Mich., assignor to Ethyl Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application August 10, 1956v Serial No. 603,227

6 Claims. (Cl. 44--69) This invention relates to improved liquid fuel for spark ignition internal combustion engines and to composite additives for such fuel.

In recent years there has been a marked trend in the automotive industry of utilizing high compression spark ignition engines in passenger cars and trucks. With such engines the accumulation of engine deposits results in a number of serious problems, includingispark plug fouling and surface ignition (also known as deposit-induced auto ignition or wild ping). Spark plug fouling results from the formation of conductive deposits on the firing end of spark plugs which provide a conductive surface for the electrical charge so that the decrease in resistance results in an insufficient potential across the spark plug electrodes. Under such circumstances the production of a spark at the spark gap is prevented. Surface ignition is erratic ignition produced by glowing engine deposits and manifests itself in reduced efficiency of operation, loss of power and of fuel economy and in increased wear of engine parts.

A critical limitation imposed upon any additive to be used in alleviating spark plug fouling or controlling surface ignition is that it must not destroy an appreciable amount of the alkyl lead antiknock compound-s which are employed in gasoline. Failure to meet this limitation causes, among other things, loss of gasoline octane quality, a property which is needed in these days of the high compression engine. Another adverse effect caused by an additive which destroys the antiknock effectiveness of alkyllead antiknock agents is the substantial economic waste caused thereby.

An object of this invention is to provide composite additives for gasoline capable of substantially reducing spark plug fouling and surface ignition without causing loss of antiknock effectiveness. Another object is to provide improved gasoline compositions having the above properties. ent from the ensuing description.

The above and other objects are accomplished by providing a gasoline additive consisting essentially of an Other objects of this invention will be appar- 2 I organic halide scavenger capable of reacting with th lead during combustion in a spark ignition internal combustion engine to form relatively volatile lead halide, and a trialkylphosphate in which each alkyl group contains from S to 8 carbon atoms and is branched on a carbon atom other than the alpha carbon atom, each branch being from 1 to 2 carbon atoms in length, the phosphate being present in the additive so that the phosphorus-tolead atom ratio is from about 0.1 :3 to about 1.6:3. Also provided by this invention is gasoline containing from about 0.53 to about 6.34 grams of lead per gallon as' an alkyllead antiknock agent, a scavenging amount of organic halide scavenger capable of reacting with the lead during combustion in a spark ignition internal combustion engine to form relatively volatile lead halide and a trialkylphosphate as defined above present in amount such that the phosphorus-to-lead atom ratio is from about 0.113 to 1.6:3.

The compositions of this invention are capable of (l) obviating ordinary knock, (2) substantially reducing surface ignition and (3) alleviating spark plug fouling because of the cooperation among the several ingredients. Moreover, these important benefits are obtainedrwith virtually no loss in antiknock effectiveness of the alkyllead ingredient.

Among the features of this invention is that the structure of the trialkylphosphate ingredient is of considerable importance insofar as effectiveness is concerned. For example, the trialkylphosphates used in the compositions present invention not only provides highly unexpected results but represents a substantial advance in the art.

To prepare the improved composite additives of this invention, the desired proportions of the ingredients are placed in a suitable container, such as a blending tank, and mixed. To insure homogeneity, use is made of conventional physical agitation, such as stirring, shaking or the like. The order of addition of the ingredients during formulation is not critical.

Representative alkyllead antiknock compositions of this invention-i. e., composite additives-are presented in Table I. The figures following the representative ingredients are parts by weight. The two figures following the trialkylphosp'hate ingredient show respectively the amounts which are used to obtain a eompositionhaving a phosphorus-to-lead atom ratio of 0.13 and 1.613. If the lower figure is doubled, the resulting composition will have a phosphorus-to-lead atom ratio of 0.223, whereas one-fourth of the second figure provides a cornposition having a phosphorus-to-lead atom ratio of 0.423. For other phosphorus concentrations, the proper adjustalkyllead antiknock agent, a scavenging amount of an ments are evident.

Table I.Antikn0ck fluid compositions Antiknock agent Scavenger Trialkylphosphate Tetramethyllead 267 Ethylene dibromide 2 Tetramethyllead 267.

Tetraethyllead 323 Tetraethyllead 3231 Tetraethyllead 323. Tetraethyllead 323. Tetraethyllead 323 Tetraethyllead 323 Tetraethyllead 323 Tetraethyllead 323 Tetrapropyllead 379 Dimethyldiethyllead 295. Methyltriethyllead 309..

fl,fi-Dibromodiisopropyl ether and 6,5

1,4-Dibromobutaue 108 and 1,4-dichlorobutaue 127. Acetylene tetrabromide 346 fl,B-Dibromodiethylether 232 dichlorodiethyl ether 143.

Tri-(Z-methylamyDphosphate 10.7171.7. Tri-(4-methylamyl)phosphate10.7-171.7. Tri-(2-methylbutyl)phosphate 103-1643. Tri-(3-methylbutyl)phosphate 103-1642.

Tri-(Z-ethylhexyl)phosphate 11.7186.7.

T1i-(3-ethylamyl)phosphate112-1792.

Tri-(5-methylheptyl)phosphate 11.7-1867.

Tri-(4-ethylhexyl)phosphate ll.7186.7

Tri-i3-methylamyl)phosphate10.7171.7. (31%1gtl11glbutyD-di-(2-methylbutyl)phosphate Tri-i4-metliylhexyl) phosphate 112-1792. Tri-(fi-methylhexyl) phosphate 11.2179.2.

'blended with the fuel. 'blend with the fuel each of the ingredients of the above The antiknock fluid compositionsshown in Table I are presented for illustrative purposes only. Other antiknock fluid compositions will now be apparent to one skilled in the art.

A variety of blending procedures are available to prepare the improved fuel compositions of this invention. For, example, a composite additive of this invention such as described in Table I can be blended in appropriate concentration with gasoline to' provide a finished fuel of this' invention containing from about 0.53 to about 6.34 grams of lead per gallon. Another method is to add an appropriate concentration of a phosphate separately to the fuel before, after or at the same time a conventional alkyllead antiknock fluid composition is Still another procedure is to composite additives separately or in various sub-combinations in any sequence. Suitable base stock gasolines used in formulating the improved finished fuels of this invention 'are illustrated by the following:

Base Fuel A.-A blend of straight-run, catalytically cracked and polymer stocks. Initial boiling point 98 F.; endpoint 402 F.

'Base Fuel B.A 100% catalytically cracked gasoline having an initial boiling point of 105 F. and an endpoint of 425 F.

Base Fuel C.-An aviation gasoline of Grade 100/ 130 comprising isopentane, alkylate, aromatics and straightrun gasoline. 'Initial boiling point 82 F.; endpoint 330 F.

Base Fuel D.-A blend of light catalytically cracked naphtha, polymer stock, catalytic reformate and light straight-run naphtha containing butane to the proper Reid vapor pressure. Initial boiling point 90 F.; endpoint 368 F.

To illustrate the effectiveness of the'impro'ved antiknock fluids of the present invention, consideration was given to the problem of spark plug fouling. In order to do this recourse was made to the following general test procedure utilizing a standard modern V8 engine equipped with overhead valves having a 3%" bore, a 3 5 stroke, a 303.7 cubic inch displacement and a compression ratio of 7.25 to l equipped with commercially available spark plugs. In order to establish a baseline, this engine was operated in conjunction with an engine dynamometer on a commercially-available fuel containing 3 milliliters of tetraethyllead per gallon as a conventional antiknock fluid containing 0.5 theory of bromine as ethylene dibromide and 1.0 theory of chlorine as ethylene dichloride. In this regard, a theory of halogen 'is the amount required to react stoichiometrically with the lead to form the corresponding lead dihalide. This engine was operated under a durability schedule used for spark plug deposit accumulation patterned after road conditions experienced in city driving which are known to produce spark plug fouling of the greatest magnitude. Such operation was substantially continuous until a number of spark plug failures was detected thereby establishing a quantitative measure of the degree of spark plug fouling which can be expressed in average hours to plug failure. The engine was then freed from deposits and equipped with new spark plugs. The same procedure was repeated using the same fuel base stock to which was added an improved antiknock fluid of the present invention. For comparative purposes another test was conducted utilizing a trialkylphosphate without the realm of the present invention, but which bears a superficial resemblance to the branched chain phosphates utilized as organolead adjuvants in this invention. At the termination of the test procedures, it was possible to obtain difference in hours between the time required to producespark plug fouling with three different antiknock fluids. The following examples more specifically illustrate the beneficial effect attending the use of an improved antiknock fuel of this invention.

EXAMPLE 1 To 300 gallons of a petroleum hydrocarbon fuel available as an article of commerce was added 900 milliliters of tetraethyllead in a fluid containing tetraethyllead, 0.5 theory of bromine as ethylene dibromide and 1.0 theory of chlorine as ethylene dichloride. The resulting blend was intimately mixed producing a homogeneous fuel composition containing 3.0 milliliters of tetraethyllead per gallon. The standard V-8 engine described hereinbefore was then operated on this fuel composition until a spark plug failure was detected. At this time the engine was shut down and the fouled spark plug was removed and replaced with a new spark plug. The engine was then operated in the same manner until a second plug failure was detected at which time the engine was shut down and the fouled plug was removed and replaced with a new one. This procedure was repeated until a third spark plug failure was produced. It was found that the average time to the three spark plug failures was 36 hours. The entire procedure was then repeated twice more with the same engine and the same fuel composition and it was found that the average time to spark plug fouling amounted to 32 and 33 hours of engine oper ation. Therefore, the average time tospark plug failures amounted to 34 hours.

EXAMPLE 2 To 300 gallons of the same fuel base stock was added 900 milliliters of tetraethyllead as a fluid comprising 0.5 theory of bromine as ethylene dibromide and 1.0 theory of chlorine as ethylene dichloride. Also added was 0.2 theory of phosphorus as tri-(2-ethylhexyl) phosphate, i. e. the phosphorus-to-lead atom ratio was 0.413. The resulting blend was then intimately mixed producing a homogeneous fuel composition containing 3.0 milliliters of tetraethyllead per gallon. Theengine was then operated on this fuel composition until three spark plug failures were detected. It was found that the average time required for such failures was 103 hours. Thus, the improvement in spark plug performance produced by the utilization of an improved fuel of thepresent invention amounted to an increase of 303 percent of the baseline.

As the data in the above examples show, the compositions of this invention result in a considerable improvement in spark plug performance. When the same test procedure was conducted on a superficially related phosphate, trimethylphosphate, in an identical concentration of phosphorus, it was found that the relative improvement amounted to 133 percent of the baseline. Consequently, the compositions of this invention are far more effective in alleviating spark plug fouling than a phospirate-containing composition suggested heretofore.

When operating an internal combustion engine on an improved gasoline of the present invention, a marked reduction in surface ignition rate is achieved. As in the case of the obviation of other deposit-induced problems, it is preferred to utilize the composite additives of this invention in high octane quality fuel, because of the fact that most of such problems exist on combustion of such fuels.

Another outstanding characteristic of the improved compositions of this invention is that in use there is essentially no adverse effect on the antiknock effectiveness of the alkyllead antiknock agent during the cooperation of this agent and the trialkylphosphates described above. This exceptional characteristic of these trialkylphosphate additives was clearly shown by conducting a series of comparative engine tests.

In the present tests the amount of tetraethyllead antagonism exhibited by triisoamyl phosphate and tri-(Z- ethylhexyl) phosphate was determined by the standard AsTM Research method, Test Proced re 13 0 1 (which can be found in the 1952 edition of ASTM Manual of Engine Test Methods for Rating Fuels). For comparative purposes, identical tests were run using triethyl phosphate and triisobutyl phosphate, additive described heretofore as being useful in leaded gasolines. The experiments consisted of blending with individual portions of a standard base fuel, 3.0 milliliters of tetraethyllead per gallon as an antiknock fluid consisting essentially of tetraethyllead, 0.5 theory of bromine as ethylene dibromide and 1.0 theory of chlorine as ethylene dichloride. To each of these fuel portions was added an amount of trialkylphosphate such that the phosphorus-to-lead atom ratio was 0.4:3. The test fuel used had a volume percent composition as follows: diisobutylene, toluene, 20%; isooctane, 20% and n-heptane, 40%.

The triisoamyl phosphate used in these tests was prepared from a fermentation amyl alcohol containing 85 percent of3-methyl butanol and 15 percent of 2-methyl butanol on a weight basis.

The results of the above tests, shown in Table II, are expressed in terms of the percent of tetraethyllead antiknock effect destroyed on conducting the above ASTM method.

Table II.Efiect of phosphorus additives on tetraethyllead antiknock efiectiveness Percent tetraethyllead effect destroyed Phosphorus additive The above data clearly show that the tetraethyllead antagonism of triisobutyl phosphate and triethyl phosphate is several times that of triisoamyl phosphate and tri-(Z-ethylhexyl) phosphate. For example, triisoamyl phosphate exhibits only one-fourth of the tetraethyllead antagonism of triethyl phosphate. Thus, the tetraethyllead antagonism is reduced by 75 percent when triisoamyl phosphate is added to the fuel in lieu of triethyl phosphate. Similarly, an improvement of about 57 percent is brought about when tri-(2-ethylhexyl) phosphate replaces triisobutyl phosphate as an additive.

The preeminence of the trialkyl phosphate additives of this invention, from the standpoint of their compatibility with alkyllead antiknock agents during engine combustion, was further demonstrated by conducting another series of engine tests. In this instance the standard ASTM Motor method, Test Procedure D357 (which can be found in the 1953 Edition of ASTM Manual of Engine Test Methods for Rating Fuels) was used. The gasoline used had an octane number cleari. e., unleaded-of 71.4. For the present tests, the gasoline samples each contained 3 milliliters of tetraethyllead per gallon, 0.5 theory of bromine as ethylene dibromide and 1.0 theory of chlorine as ethylene dichloride. A sample of this leaded gasoline was subjected to the above ASTM test method and the octane number of the fuel determined. Then, representative fuels of this invention were subjected to the same test procedure. These particular fuels contained either triisoamyl phosphate or tri-(Z-ethylhexyl) phosphate in amount such that the phosphorus-to-lead atom ratio was 1:3. For comparative purposes, another sample of leaded gasoline which contained the same concentration of phosphorus as triisobutyl phosphate-an additive suggested in the prior art-Was rated under the same conditions. The results of these tests are shown in Table III.

Table IlI.Efiect of phosphorus additives on tetraethyllead anziknock effectiveness Octane Change Phosphorus additive number in octane number None 84. 0 Additives of the invention:

Triisoamyl phosphate 83. 4 -0. 6 'Iri-(2-ethylhexyl) phosphate. 83.5 0. 5 Additives not of the inventi obutyl phosphate 82. 7 1. 3

The data shown in Table III establish that the. trialkylphosphate additives of this invention exhibited practically no adverse effect upon the antiknock effectiveness of tetraethyllead, whereas a closely-related trialkylphosphate shown in the prior art caused a significant amount of this adverse effect. Thus, the compositions of this invention result in the virtual elimination of deposit-induced engine problems without incurring any significant amount of alkyllead antagonism.

The alkyllead antiknock agents which are present in the compositions of this invention are represented by such compounds as tetramethyllead, tetraethyllead, tetrapropyllead, tetrabutyllead, diethyldimethyllead, triethylmethyllead, and the like, or mixtures thereof. Such compounds containing from 4 to about 16 carbon atoms, one atom of lead and a plurality of lead-to-carbon bonds, are capable of increasing the octane quality of gasoline when employed therein in antiknock quantitiesabout 0.53 to about 6.34 grams of lead per gallon. Of such compounds, tetraalkyllead compounds having 4 to about 12 carbon atoms have superior volatility characteristics from the standpoint of engine induction and are thus preferred. Halogen-containing alkyllead compounds, such as triethyllead bromide, may also be used in the compositions of this invention.

As stated above the trialkylphosphates used in this invention are those in which each alkyl group contains from 5 to 8 carbon atoms and is branched on a carbon atom other than the alpha carbon atom, each branch being from 1 to 2 carbon atoms in length. Thus, these trialkylphosphates are further characterized in that they contain a total of from 15 to 24 carbon atoms in the molecule. Typical trialkylphosphates useful in the practice of this invention include tri-(Z-methylbutyl) phosphate; tri-(3- methylbutyl) phosphate; tri-(Z-ethylhexyl) phosphate; tri-(Z-methylamyl) phosphate; tri-(4-methylamyl) phosphate; tri-(3-ethylamyl) phosphate; tri-(S-methylheptyl) phosphate; tri-(3-ethylhexyl) phosphate; tri-(4-ethylhexyl) phosphate; (Z-methylbutyl)-di-(3-methylbutyl) phosphate; tri-(3-methylamyl) phosphate; (3-methylbutyl)- di-(Z-methylbutyl) phosphate; tri-(4-methylhexyl)-v phosphate; tri-(S-methylhexyl) phosphate; and the like. The methods for the preparation of these phosphorus compounds will be familiar to one skilled in the art. In general, the processes involve interaction between a phosphorus oxy halidee. g., POCl and the corresponding branched monohydric alcohol. For further details regarding the preparation of such branched chain alkyl phosphates, see Kosolapoff, Organophosphorus Compounds. A feature of this invention is the fact that many of the above phosphates are available as articles of commerce, frequently in the form of mixtures, and that such mixtures can be successfully used.

As pointed out above, the trialkylphosphates are used in the compositions of this invention in amounts such that the phosphorus to-lead atom ratio is from about 0.1:3 to about 1.623. However, generally speaking, it is sufficient to employ an amount of these phosphates such that the phosphorus-to-lead atom ratio is from about 0.223 to about 1:3.

The scavengers which are present in the compositions of this invention are organic halide compounds which react with the lead during combustion in the engine to form volatile lead halide. The halogen of these scavengers has an atomic weight between 35 and 80; that is, the active scavenging ingredient is chlorine and/or bromine. Such scavengers include ethylene dibromide; ethylene dichloride; carbon tetrachloride; propylene dibro mide; 2 chloro- 2,3 dibromobutane; 1,2,3 tribromopropane; hexachloropropylene; mixed bromoxylenes; 1,4-dibromobutane; 1,4-dichloropentane; f3,;8-dibromodiisopropyl ether; 13,;30-dichlorodiethyl ether; trichlorobenzene; dibromotoluenesi' tert-butyl bromide; 2-methyl-2- bromobutane; 2,3,3-trimethyl2-bromobutane; tcrt-butyl chloride; 2,3-dimethyl-2,3-dibromobutane; 2,3-dimethyl- 2,5 dibromohexane; 2 methyl 2,3 dibromobutane; -2 methyl 2,3 dichloroheptane; 2 methyl 2,4 dibromohexane; 2,4dibromopentane; 2,5-dichlorohexane; 3 methyl 2,4 dibromopentane; 1 phenyl 1 bromoethane; 1 phenyl 1 chloroethane; ethyl abromoacetate; diethyl-dibromomalonate; propyl-a-chlorobutyrate; 1,1-dichloro-1-nitroethane; 1,1-dichloro-2-nitroethane; 1,l-dibromo-l-nitrobutane; 2-chloro-4-nitropentane; 2,4-dibromo-3-nitropentane; 1-chloro-2-hydroxyethane; 1-bromo-3-hydroxypropane; 1-bromo-3-hydroxybutane; 3-methyl-2-bromo-4-hydroxypentane; 3,4-dimethyl- 2-bromo-4-hydroxypentane; and, in general, scavengers disclosed in U. S. Patents 1,592,954; 1,668,022; 2,364,921; 2,479,900; 2,479,901; 2,479,902; 2,479,903; and 2,496,983. In short, it is preferred to employ halogenated scavengers containing only carbon and elements selected from the group consisting of hydrogen, bromine, chlorine, nitrogen and oxygen. Particularly preferred scavengers are halohydrocarbons; that is, bromohydrocarbons, chlorohydrocarbons, and bromochlorohydrocarbons having a vapor pressure frm 0.1 to 250 millimeters of mercury at 50 C. The total amount of scavenger used is preferably from about 0.5 to about 2.0 theories, a theory being defined as the quantity required to react with the lead to form lead halide-i. e., 2 atoms of halogen per atom of lead. This amount can be in the form of a single compound or a mixture of compounds. However, when I use mixtures of bromine-containing and chlorine-containing scavengers, particularly bromoand chlorohydrocarbons as the scavenger complement, I can employ a wider range of concentrations in the proportions described in U. S. Patent 2,398 ,281. Thus, the scavenger concentrations used are those which are suificient to control the amount of deposits formed in the engine, particularly on the exhaust valves.

The antiknock compositions of this invention can contain other ingredients, such as dyes for identification purposes; metal deactivators, such as N,N-disalicylidene- 1,2-diaminopropane, etc.; other surface ignition control additives; anti-icing and anti-rust additives; upper cylinder lubricants; induction system cleanliness agents; antioxidents, such as N,N'-di-sec-butyl-p-phenylene diamine, p-alkylamino phenols, alkyl phenols, and the like.

My antiknock fluids may be used in a variety of hydrocarbon base stocks boiling within or throughout the gasoline boiling range. This range is from about 80 to about 420 F. for motor gasolines, while the endpoint of aviation fuels is in the order of about 310-335 F. Thus, the improvements can be made in fuels resulting from thermal and catalytic cracking processes, reforming, hydroforming and alkylating procedures; in straight-run gasolines; and in various blends of gasoline hydrocarbons.

This application is a continuation-in-part of my copending application, Serial No. 365,263, filed June 30, 1953, and now abandoned.

I claim:

1. A gasoline additive consisting essentially of an alkyllead antiknock agent, a scavenging amount of an organic halide scavenger capable of reacting with the lead during combustion in a spark ignition internal combustion engine to form relatively volatile lead halide, and a trialkylphosphate in which each alkyl group contains from 5 to 8 carbon atoms and is branched on a carbon atom other than the alpha carbon atom, each branch being from 1 to 2 carbon atoms in length, said phosphate being present in the additive in amount such that the phosphorusto-lead atom ratio is from about 0.113 to 1.6:3.

2. The composition of claim 1 wherein said organic halide scavenger is a mixture of ethylene dibromide and ethylene dichloride.

3. A gasoline additive consisting essentially of tetraethyllead, about 0.5 theory of bromine as ethylene dibromide, about 1.0 theory of chlorine as ethylene dichloride, and a trialkphosphate in which each alkyl group contains from 5 to 8 carbon atoms and is branched on a carbon atom other than the alpha carbon atom, each branch being from 1 to 2 carbon atoms in length, said phosphate being present in the additive in amount such that the phosphorus-to-lead atom ratio is from about 0.123 to 1.623.

4. Gasoline containing from about 0.53 to about 6.34 grams of lead per gallon as an alkyllead antiknock agent, a scavenging amount of an organic halide scavenger capable of reacting with the lead during combustion in a spark ignition internal combustion engine to form relatively volatile lead halide and a trialkylphosphate in which each alkyl group contains from 5 to 8 carbon atoms and is branched on a carbon atom other than the alpha carbon atom, each branch being from 1 to 2 carbon atoms in length, said phosphate being present in the gasoline in amount such that the phosphorus-to-lead atom ratio is from about 0.1:3 to 1.623.

5. The composition of claim 4 wherein said organic halide scavenger is a mixture of ethylene dibromide and ethylene dichloride.

6. Gasoline containing from about 0.53 to about 6.34 grams of lead per gallon as tetraethyllead, about 0.5 theory of bromine as ethylene dibromide, about 1.0 theory of chlorine as ethylene dichloride, and a trialkylphosphate in which each alkyl group contains from 5 to 8 carbon atomsand is branched on a carbon atom other than the alpha carbon atom, each branch being from 1 to 2 carbon atoms in length, said phosphate being present in the gasoline in amount such that the phosphorus-to-lead atom ratio is from about 0.1 :3 to 1.6:3.

References Cited in the file of this patent UNITED STATES PATENTS 2,340,331 Knutson et al. Feb. 1, 1944 2,375,218 Fry et al. May 8, 1945 2,405,560 Campbell Aug. 13, 1946 2,427,173 Withrow Sept. 9, 1947 2,543,514 Van Hartesveldt Feb. 27, 1951 2,765,220 Yust et al. Oct. 2, 1956 FOREIGN PATENTS 600,191 Great Britain Apr. 2, 1948 683,405 Great Britain Nov. 26, 1952 OTHER REFERENCES Ind. and Eng. Chem., March 1951, vol. 43, No. 3, Antiknock Antagonists by Livingston, pp. 663-670. 

4. GASOLINE CONTAINING FROM ABOUT 0.53 TO ABOUT 6.34 GRAMS OF LEAD PER GALLON AS AN ALKYLLEAD ANTIKNOCK AGENT, A SCAVENGING AMOUNT OF AN ORGANIC HALIDE SCAVENGER CAPABLE OF REACTING WITH THE LEAD DURING COMBUSTION IN A SPARK IGNITION INTERNAL COMBUSTION ENGINE TO FORM RELATIVELY VOLATILE LEAD HALIDE AND A TRIALKYLPHOSPHATE IN WHICH EACH ALKYL GROUP CONTAINS FROM 5 TO 8 CARBON ATOMS AND IS BRANCHED ON A CARBON ATOM OTHER THAN THE ALPHA CARBON ATOM, EACH BRANCH BEING FROM 1 TO 2 CARBON ATOMS IN LENGTH, SAID PHOSPHATE BEING PRESENT IN THE GASOLINE IN AMOUNT SUCH THAT THE PHOSPHORUS-TO-LEAD ATOM RATIO IS FROM ABOUT 0.1:3 TO 1.6:3. 